Quantitative functional MRI of the visual cortex as a function of luminance contrast at 1.5 T

Examined the BOLD signal changes in primary visual cortex as a function of luminous contrast at 1.5 T in 4 normals and 2 patients with multiple sclerosis (MS) disease. Echo planar T2* weighted BOLD imaging experiments were performed using a 1.5 T Imager. Ten axial slices through the calcarine fissure were obtained. The imaging series consisted of alternations between a 20-second epoch of dark screen (rest) and a 20-second epoch of a flickering checkerboard (activation) repeated 6 times. Each imaging series utilized a stepwise, graded increase of eight different luminance contrast levels. A paired t-test was used to compare the control condition with each activation condition. The data shows a linear trend in the number of fMRI activated voxels within the visual cortex with increasing luminous contrast in normals and MS patients. This study demonstrates quantifiable changes in BOLD signal and a linear increase in activated voxels within the primary visual cortex with increasing luminous contrast.